Ultrasonic attenuation materials

ABSTRACT

Improved acoustic attenuation materials and applications are provided. An improved acoustic attenuation material may include a woven layer of fibers made of porous polymers, such as porous polytetrafluoroethylene (PTFE), that include interstitial space. An improved acoustic attenuation material may include sheets of porous polymers interleaved with layers of epoxy. The sheets of porous polymers may include through holes. An embodiment of an ultrasonic transducer that includes a backing with woven layers of porous PTFE fibers is provided. The ultrasonic transducer that includes a backing with woven layers of porous PTFE fibers may be used in a three-dimensional ultrasound imaging apparatus. An embodiment of an ultrasonic transducer that includes a plurality of sheets of porous PTFE interleaved with layers of epoxy is provided. The ultrasonic transducer that includes a plurality of sheets of porous PTFE may be used in an ultrasonic imaging catheter.

RELATED APPLICATION

The present application is a divisional application of allowed U.S.patent application Ser. No. 11/694,453 filed Mar. 30, 2007 now U.S. Pat.No. 7,956,514.

BACKGROUND

Acoustic attenuation materials are used in a wide variety ofapplications where it is desired to attenuate acoustic signals. Acousticattenuation material may be used, for example, in soundproofingmaterials used in architectural applications. Many such acousticattenuation materials require considerable volume to achieve desiredlevels of attenuation.

Acoustic attenuation materials are also incorporated into relativelysmall devices where control of acoustic energy is required. One suchapplication is in the field of ultrasound imaging probes. Ultrasoundimaging probes continue to enjoy widespread use in the medical field. Byway of example, ultrasound probes are utilized for a wide variety ofexternal, laparoscopic, endoscopic and intravascular imagingapplications. The ultrasound images provided by imaging probes may, forexample, be used for diagnostic purposes.

Ultrasound imaging probes typically include a plurality of parallelpiezoelectric transducer elements arranged along a longitudinal axis,with each element interconnected to a pair of electrodes. Typically, thetransducers are subdivided in the longitudinal direction by dicingduring production, resulting in independent transducer elements thatenable electronic steering and focusing within an imaging plane. Anelectronic circuit, interconnected to the electrodes, excites thetransducer elements causing them to emit ultrasonic energy. Thetransducer elements may be operable to convert received ultrasonicenergy into electrical signals, which may then be processed and used togenerate images.

Typically, the transducers include an active layer of a piezoelectricmaterial with an acoustic face from which acoustic signals are emitted.Often an acoustic damping member is disposed rearward of the activelayer on an opposite side of the active layer from the acoustic face.The acoustic damping member serves to damp undesirable acoustic signals(e.g., signals that may emanate from and be reflected back to the rearface of the transducer) that may interfere with the acoustic signalsreceived at the acoustic face. As may be appreciated, for a particularacoustic damping material, acoustic damping capabilities typicallyincrease as the volume of the acoustic damping member increases.Accordingly, as the acoustic damping member is reduced in volume, theacoustic damping capabilities typically decrease. Consequently, theoverall volume and mass of an ultrasound probe that includes anultrasonic transducer and acoustic damping member may be at leastpartially dependent on the acoustic damping capabilities of the materialof the acoustic damping member.

SUMMARY

As the applications for, and use of, ultrasound imaging probes continueto expand, so does the need for ultrasound probe designs that yieldhigher imaging performance, greater miniaturization, and/or increasedproduction efficiencies. In this regard, the ability to realize enhancedperformance, miniaturization and production efficiencies related toultrasound imaging probes through improvements to acoustic attenuationmaterials used in ultrasound imaging probes becomes particularlysignificant. Moreover, there exists a need for improved acousticattenuation materials in general.

In view of the foregoing, an object of embodiments described herein maybe to provide improved acoustic attenuation materials. An additionalobjective may be to provide improved ultrasonic transducer systemsutilizing improved acoustic attenuation materials.

In one aspect, an acoustic attenuation material is provided operable toattenuate acoustic energy incident upon the material. The material mayinclude a first component comprised of a first polymer having a porosityand a second component comprised of a second polymer. The porosity ofthe first component may be partially filled with the second component.The first component may have a first flexural modulus when its porosityis free from the second component and a second flexural modulus when thesecond component is partially disposed within its porosity. The firstflexural modulus may be lower than the second flexural modulus. Thefirst component may be comprised of a woven and/or non-woven porouspolymer.

In another aspect, an acoustic attenuation material comprising a firstlayer adapted for use in attenuating acoustic energy having a frequencybetween 100 kHz and 100 MHz is provided. The first layer may have afirst stiffness and a first acoustic attenuation. The acousticattenuation material may also include a second layer having a secondstiffness and a second acoustic attenuation. The first stiffness may beless than the second stiffness and the first acoustic attenuation may beat least two times greater than the second acoustic attenuation. Thefirst layer may be comprised of woven and/or non-woven porous polymer.

In a related aspect, an acoustic attenuation material including a wovenlayer is operable to attenuate acoustic energy incident upon thematerial. The woven layer may be comprised of a plurality of fibers. Thefibers may be comprised of porous polytetrafluoroethylene (PTFE). Thewoven layer may define void space between the fibers that may be atleast partially filled with fluorothermoplastic (THV).

In still another aspect, an acoustic attenuation material is providedthat is operable to attenuate acoustic energy incident upon the materialthat is comprised of a plurality of non-woven membranes and a pluralityof support layers. The non-woven membranes may be comprised of a porouspolymer. The plurality of non-woven membranes may be interleaved withthe plurality of support layers. The support layers may be comprised ofa support material. The support material may be porous or non-porous.The support layers may be porous or non-porous.

In a further aspect, an acoustic attenuation material is provided thatis configured such that a sound beam traveling from a first side of thematerial to a second side of the material must pass through at least aportion of a porous polymer. A reinforcing material may also be includedin the acoustic attenuation material. The acoustic attenuation of theporous polymer may be at least twice that of the reinforcing material.

In another aspect, a method is provided that includes the steps ofplacing a member comprising a layer of porous polymer in the path ofacoustic energy to be attenuated, absorbing at least a portion of theacoustic energy within the member and supporting the layer of porouspolymer with at least one layer of a support material. The porouspolymer may be woven and/or non-woven. The method may further includelocating a front side of the material adjacent to a surface andabsorbing both energy emanating from the surface and energy incidentupon a back side of the material within the material. The method mayalso include attenuating acoustic energy within a predetermined volumeby placing the material within the predetermined volume.

In still another aspect, an acoustic attenuation material is providedcomprising a woven layer adapted for use in an ultrasonic transducerapparatus and a reinforcing material. The woven layer may be operable toattenuate acoustic energy incident upon it. The woven layer may becomprised of a plurality of porous fibers that define void space betweenthe plurality of fibers. The reinforcing material may at least partiallyfill the void space.

An embodiment may include a second woven layer comprising a secondplurality of fibers. The second plurality of fibers may be porous andmay define second woven layer void space. The reinforcing material mayat least partially fill the second woven layer void space. In variousembodiments, a layer of epoxy may be disposed between two woven layers.

In an embodiment, the reinforcing material may comprise epoxy, THV,Fluorinated Ethylene-Propylene (FEP), PTFE, polyethersufone (PES),ethylene-FEP copolymer (EFEP), polyester thermoplastic (PET),polyetheretherketone (PEEK), polyetherimide (PEI), polycarbonate (PC),liquid crystal polymer (LCP) or any combination thereof. In anembodiment, the plurality of fibers may comprise a porous polymerselected from a group consisting of PTFE, urethane, polystyrene,fluoropolymer, silicone and polyolefin.

The acoustic attenuation material may, in an embodiment, be operable toattenuate acoustic energy in the ultrasonic range. For example, theacoustic attenuation material may be operable to attenuate acousticenergy between 100 kHz and 100 MHz.

In another aspect, an ultrasound transducer system is providedcomprising an active layer and an acoustic attenuation layer. The activelayer may have an acoustic face and a rear face (opposite of theacoustic face) and include at least one ultrasonic transducer element.The acoustic attenuation layer may comprise a porous polymer and areinforcing material and be interconnected to the rear face of theactive layer. In an arrangement, the reinforcing material may bepartially imbibed into the porosity of the porous polymer.

In an embodiment, the ultrasonic transducer elements may be operable totransmit ultrasonic signals, receive ultrasonic signals, or bothtransmit and receive ultrasonic signals. At least one of the ultrasonictransducer elements may be planar. At least one of the ultrasonictransducer elements may be curved. In an embodiment, the reinforcingmaterial may include a thermoplastic material and/or a thermosetmaterial.

The ultrasound transducer system of various embodiments may include anintermediate layer disposed between the rear face of the active layerand the acoustic attenuation layer. The intermediate layer may compriseepoxy, silicone rubber, tungsten, aluminum oxide, mica, microspheres, orany combination thereof.

In yet another aspect, an ultrasound transducer system is providedcomprising an active layer and an acoustic attenuation layer. The activelayer may have an acoustic face and a rear face (opposite of theacoustic face) and include at least one ultrasonic transducer element.The acoustic attenuation layer may include a woven layer of porouspolymer fibers and a reinforcing material and be interconnected to therear face of the active layer. The reinforcing material may at leastpartially fill void space between fibers of the acoustic attenuationlayer. In an arrangement, the acoustic attenuation layer may containmultiple woven layers with layers of adhesive between adjacent acousticattenuation layers to bind the acoustic attenuation layers together.

An embodiment may include an electrical connection member. Theelectrical connection member may be comprised of an insulating materialand a plurality of independent electrically conductive pathways. Each ofthe plurality of electrically conductive pathways may be disposedtransverse to and in electrical contact with a corresponding one of theat least one ultrasonic transducer elements.

In an arrangement, the backing may include a plurality of continuouspathways through the backing. The passageways may be at least partiallyfilled with an electrically conductive material and provide anelectrically conductive path through the backing.

In another aspect, an ultrasound transducer system is providedcomprising an active layer and a backing. The active layer may have anacoustic face and a rear face (opposite of the acoustic face) andinclude at least one ultrasonic transducer element. The backing mayinclude a support material. The backing may include at least onenon-woven membrane comprised of a porous polymer interleaved with aplurality of support layers comprised of the support material.

In an embodiment, the non-woven membranes may contain a plurality ofthrough holes at least partially filled with the support material.Adjacent non-woven membranes may be arranged such that at least some ofthe plurality of through holes of a particular non-woven membrane arefree from alignment with any of the through holes of an adjacentnon-woven membrane. Adjacent non-woven membranes may be arranged suchthat most or all of the plurality of through holes of a particularnon-woven membrane are free from alignment with any through holes of anadjacent non-woven membrane. In an embodiment, each of the non-wovenmembranes may be less than 200 microns (e.g., between 1 and 200 microns)thick and each of the plurality of support layers may be less than 200microns (e.g., between 1 and 200 microns) thick.

In an embodiment, each of the membranes and support layers may beoriented parallel to the active layer. In another embodiment, each ofthe membranes and support layers may be oriented at an angle relative tothe active layer.

In an embodiment, the membranes and support layers may be free fromthrough holes. In such an arrangement, each of the non-woven membranesmay be less than 800 microns (e.g., between 1 and 800 microns) thick andeach of the plurality of support layers may be less than 500 microns(e.g., between 1 and 500 microns) thick. Also, in such an arrangement,the support material may be comprised of polymer, ceramic, metal or anycombination thereof. The support material may be porous or non-porous.The plurality of support layers may be porous or non-porous. Inembodiments where the support material comprises polymer, the polymermay be thermoset, thermoplastic, fluoropolymer, epoxy or any combinationthereof. Furthermore, a plurality of interconnection layers may bedisposed between adjacent membranes and support layers. Theinterconnection layers may comprise a carrier with adhesive disposed onboth sides. The interconnection layers may bind adjacent membranes andsupport layers together.

In still another aspect, an ultrasound transducer system is providedcomprising an active layer and a backing. The active layer may have anacoustic face and a rear face (opposite of the acoustic face) andinclude at least one ultrasonic transducer element. The backing mayinclude a first side and a second side oppositely disposed from thefirst side. The backing may be interconnected to the rear face of theactive layer. The backing may include porous polymer and reinforcingmaterial and be configured such that a sound beam traveling from thefirst side to the rear face of the ultrasonic transducer element mustpass through at least a portion of the porous polymer. The porouspolymer and reinforcing material may be selected such that the overallflexural modulus of the backing is at least twice that of the porouspolymer alone. With respect to sound beams traveling from the first sideto the rear face, the backing may have an acoustic attenuation of atleast 25 dB/cm at 1 MHz. The porous polymer and reinforcing material maybe selected such that the acoustic attenuation of the porous polymer isat least twice that of the reinforcing material.

In another aspect, an ultrasound transducer system is providedcomprising an active layer and a backing. The active layer may have anacoustic face and a rear face (opposite of the acoustic face) andinclude at least one ultrasonic transducer element. The backing mayinclude a plurality of membranes comprised of a porous polymerinterleaved with a plurality of support layers comprised of a supportmaterial. The plurality of membranes may include a plurality of sectionsfrom which portions of the plurality of membranes have been removed.

Adjacent membranes may be arranged such that some, most, or all of theplurality of sections from which portions of the plurality of membraneshave been removed of a particular membrane are free from alignment withany of the through holes of an adjacent membrane.

In even another aspect, a method of reducing acoustic energy incident ona back face of an ultrasound transducer is provided. The method mayinclude providing a layer of material comprising a porous polymer,locating the layer of material adjacent to a back face of an ultrasoundtransducer and absorbing acoustic energy within the layer of material.The layer of material may have a front surface and a rear surface. Thefront surface may be in face to face contact with the back face of theultrasound transducer while the rear surface may be in contact with afluid. The absorbing may include absorbing acoustic energy emanatingfrom the back face of the ultrasound transducer and absorbing acousticenergy incident upon the rear surface of the layer of material.

In an embodiment, the fluid may be a gas or a liquid. In an embodiment,the layer of material may comprise at least one woven layer of porouspolymer fibers wherein void space between the porous polymer fibers isat least partially filled with a non-porous polymer.

In another aspect, a method of reducing acoustic energy incident on aback face of an ultrasound transducer is provided. The method mayinclude providing an acoustic attenuation member that includes anon-woven porous polymer layer and a support material, locating theacoustic attenuation member adjacent to a back face of an ultrasoundtransducer and absorbing acoustic energy within the acoustic attenuationmember. The acoustic attenuation member may have a front surface and arear surface. The front surface may be in face to face contact with theback face of the ultrasound transducer. The absorbing may includeabsorbing, within the acoustic attenuation member, acoustic energyemanating from the back face of the ultrasound transducer and acousticenergy incident upon the rear surface of the acoustic attenuationmember.

In an embodiment, the acoustic attenuation member may comprise aplurality of non-woven porous polymer layers interleaved with aplurality of layers of the support material. The plurality of non-wovenporous polymer layers may include a plurality of holes.

In yet another aspect, an ultrasonic catheter probe is provided thatincludes an ultrasound transducer disposed within an outer shell. Theultrasound transducer includes an active layer with an acoustic face anda rear face opposite from the acoustic face. The active layer maycomprise at least one ultrasonic transducer element. The ultrasoundtransducer may further include a backing interconnected to the rearface. The backing may comprise a plurality of acoustic attenuationlayers interleaved with a plurality of support layers.

In an embodiment, the plurality of acoustic attenuation layers maycomprise a porous polymer. In an embodiment, the plurality of acousticattenuation layers may include a plurality of vias therethrough. Theplurality of vias may be at least partially filled with a supportmaterial.

In still another aspect, an acoustic attenuation device comprising anacoustic attenuation material and a support structure interconnected tothe acoustic attenuation material is provided. The acoustic attenuationmaterial may be operable to attenuate acoustic energy incident upon thematerial and may include a first component comprised of a porous polymerand a second component comprised of a support material. The firstcomponent may be woven and/or non-woven.

In an arrangement, the porosity of the porous polymer may be partiallyfilled with the second component. In an arrangement, the first componentmay be comprised of a woven layer of porous fibers.

In an embodiment, the first component may include a plurality ofnon-woven membranes and the second component may comprise a plurality ofsupport layers. The membranes and support layers may be interleaved. Inan embodiment, each of the plurality of membranes may include aplurality of vias defining a plurality of passageways through theplurality of membranes. The plurality of vias may be at least partiallyfilled with the support material.

The various features discussed above in relation to each aforementionedaspect may be utilized by any of the aforementioned aspects. Additionalaspects and corresponding advantages will be apparent to those skilledin the art upon consideration of the further description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of an ultrasound probeand a region of interest.

FIG. 2 illustrates an embodiment of a woven layer of fibers.

FIG. 3 is a cross sectional view of the woven layer of fibers of FIG. 2.

FIG. 4 is a cross sectional view of the woven layer of fibers of FIG. 2with a filler material disposed within the void space between fibers.

FIG. 5 is a cross sectional view of the woven layer of fibers of FIG. 2with a filler material disposed within the void space between fibers andmembranes disposed on the top and bottom of the woven layer.

FIG. 6 is a cross sectional view of two layers of materials, similar toas shown in FIG. 5, bonded together.

FIG. 7 is a cross sectional view of two layers of materials as shown inFIG. 4 bonded together.

FIG. 8A is a cross sectional view of a material that comprises aplurality of layers of porous polymer sheets interleaved with aplurality of sheets of support material.

FIG. 8B is a cross sectional view of a material that comprises aplurality of layers of porous polymer sheets interleaved with aplurality of sheets of support material.

FIG. 9 is an isometric view of a section of an embodiment of a sheet ofporous polymer comprising multiple through holes.

FIG. 10 is a cross sectional view of the sheet of FIG. 9.

FIG. 11 is a cross sectional view of multiple layers of the sheet ofFIG. 9 interleaved with multiple layers of support material.

FIG. 12 is an isometric view of an embodiment of an ultrasound probeassembly.

FIG. 13 is a schematic view of a portion of the ultrasonic transducer ofFIG. 12.

FIG. 14 illustrates an embodiment of an ultrasonic transducer attachedto a frame.

FIG. 15 is a cross sectional view of an embodiment of an ultrasonictransducer assembly.

FIG. 16 is schematic view of an embodiment of a backing assembly of anultrasonic transducer assembly.

FIG. 17 is a schematic view of an embodiment of an ultrasonictransducer.

FIG. 18 is an isometric view of an embodiment of an ultrasound probeassembly contained within a catheter.

FIG. 19 is a cross sectional view of the catheter of FIG. 18.

FIG. 20 is an isometric view of an acoustic attenuation materialinterconnected to a support structure.

FIG. 21 is a flow diagram of a method of attenuating acoustic energy.

FIG. 22 is a flow diagram of a method of reducing acoustic energyincident on a back face of an ultrasound transducer.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an embodiment of an ultrasound probe100, an ultrasound imaging apparatus 109 and a region of interest 102.The ultrasound probe 100 includes at least one ultrasonic transducer103. The ultrasonic transducer 103 may be a mechanically active layeroperable to convert electrical energy to mechanical (e.g., acoustic)energy and/or convert mechanical energy into electrical energy. Forexample, the ultrasonic transducer 103 may be operable to convertelectrical signals from the ultrasound imaging apparatus 109 intoultrasonic acoustic energy. Furthermore, the ultrasonic transducer 103may be operable to convert received ultrasonic acoustic energy intoelectrical signals. The ultrasonic transducer 103 may comprise at leastone ground electrode 112 and at least one signal electrode 113. The atleast one signal electrode 113 and the at least one ground electrode 112may be electrically interconnected to the ultrasound imaging apparatus109 by at least one signal connection 110 (e.g., at least one signalwire) and at least one ground connection 111 (e.g., at least one groundwire), respectively. The ultrasonic transducer 103 may comprise an arrayof individual transducer elements that may each be electricallyconnected to the ultrasound imaging apparatus 109 via a signalconnection and a ground connection. The array may be a one-dimensionalarray that includes a single row of individual transducer elements. Thearray may be a two-dimensional array that includes individual transducerelements arranged, for example, in multiple columns and multiple rowsGround connections of the entire array may be aggregated and beelectrically connected to the ultrasound imaging apparatus 109 through asingle ground connection.

To generate an ultrasound image, the ultrasound imaging apparatus 109may send electrical signals to the ultrasonic transducer 103 which inturn may convert the electrical energy to ultrasonic acoustic energy 104which may be emitted toward a region of interest 102. The region ofinterest 102 may be an internal structure of a patient, such as anorgan. The structure within the region of interest 102 may reflect aportion of the acoustic energy 106 back toward the ultrasonic transducer103. The reflected acoustic energy 106 may be converted to electricalsignals by the ultrasonic transducer 103 which may be sent to theultrasound imaging apparatus 109 where the signals may be processed andan image of the region of interest 102 may be generated.

The process of converting the electrical signals from the ultrasoundimaging apparatus 109 into ultrasonic acoustic energy 104 directedtoward the region of interest 102 may also produce additional acousticenergy 107 directed in directions other than toward the region ofinterest 102. This additional acoustic energy 107 may reflect off ofvarious structures, such as the housing 101 of the ultrasound probe 100,and return to the ultrasonic transducer 103 where it may be converted toelectrical signals. The electrical signals from the reflected additionalacoustic energy 107 may interfere with the electrical signals from thereflected acoustic energy 106. Such interference may result in imagequality degradation.

To reduce interference from the reflected additional acoustic energy107, acoustic attenuation material 108 may be included in the ultrasoundprobe 100. The acoustic attenuation material 108 may be interconnectedto the ultrasonic transducer 103 along a surface of the ultrasonictransducer 103 opposite from the surface of the ultrasonic transducer103 facing the region of interest 102 (e.g., a back surface of theultrasonic transducer 103). The acoustic attenuation material 108 mayprevent a substantial amount of the additional acoustic energy 107 fromreturning to the back surface of the ultrasonic transducer 103. Theacoustic attenuation material 108 may also reduce the amount of acousticenergy reaching the back surface of the ultrasonic transducer 103 fromother sources. In this regard, the acoustic attenuation material 108 mayprovide for reduced interference and enhanced image quality. Inembodiments where the acoustic attenuation material 108 is connecteddirectly to the ultrasonic transducer 103, the at least one signalconnection 110 may pass through the acoustic attenuation material 108.

Furthermore, acoustic attenuation material may be positioned in otherlocations within the ultrasound probe 100 to attenuate acoustic energywithin the ultrasound probe 100. For example, an amount of acousticattenuation material 114 may be placed against the housing 101 to dampen(e.g., absorb) acoustic energy that may otherwise reflect off of aninner surface of the housing 101 and reduce image quality. Althoughillustrated as lining one entire side of the inside of the housing 101in FIG. 1, the acoustic attenuation material 114 may be placed along anyinternal surface or portion thereof of the housing 101 where it may bebeneficial to attenuate acoustic energy. The acoustic attenuationmaterial 114 may also be located adjacent to other structures within theultrasound probe 100 (e.g., circuit boards) to attenuate acoustic energythat could otherwise reflect off of those other structures.

Embodiments of acoustic attenuation materials that may be used forattenuating acoustic energy, including attenuating ultrasonic energy inultrasound probes will now be described. FIG. 2 is an illustration of awoven layer 200 that may be used in an acoustic attenuation material.The woven layer 200 may be comprised of a plurality of individualfibers, such as individual fibers 202 a, 202 b, 202 c and 202 d. FIG. 2illustrates an example of a type of weave where individual fibers, suchas individual fibers 202 a, 202 b, 202 c and 202 d, alternate positionrelative to each other. For example, fiber 202 b alternates betweenbeing below fiber 202 a (as oriented in FIG. 1) at a first intersection203 a and above fiber 202 c at a second intersection 203 b.

The woven layer 200 of FIG. 2 is one example of the type andconfiguration of weave that may be used in an embodiment. Other types ofweaves known to those skilled in the art may be utilized. Also, variousparameters of the weaves may be altered to achieve different weavecharacteristics. For example, the distance between fibers, such as thedistance between fibers 202 a and 202 c may be varied to achieve variousweave densities. Other woven layer 200 characteristics, such asthickness, may be achieved by altering fiber diameters and/or theconfiguration of the weave. All of the fibers of the woven layer 200 maybe of the same diameter or the fibers may comprise a plurality ofdifferent diameters.

The woven layer 200 also includes void space. Void space is generallyany space within the plane of the weave that is not occupied by any ofthe fibers that make up the woven layer 200. For example, the space 204between fibers 202 a, 202 b, 202 c, and 202 d is part of the void spacedefined by the woven layer 200.

FIG. 3 is a cross sectional view of the exemplary woven layer 200 alongsection line A-A of FIG. 2. FIG. 3 shows the serpentine arrangementwhere individual fibers, such as fiber 202 b, alternate positionrelative to other fibers of the weave.

The individual fibers of the woven layer 200, such as fiber 202 b, maycomprise a polymer. The polymer may be configured so that the fibershave a predeterminable porosity. Porosity is a measure of theinterstitial space in a material. The interstitial space may be spacewithin the polymer that does not contain the polymer. Porosity may beexpressed as the proportion of the volume of the interstitial space inthe material to the total volume of the material. Accordingly, theporosity will be between zero and one and may be given as a percentage.A value of zero would indicate no porosity. The interstitial space maycontain air, water or any other substance. The interstitial space maycontain a vacuum. For example, the porosity of the fibers of the wovenlayer 200 may be less than 85 percent.

In an embodiment, the individual fibers may be comprised of porouspolymer, such as porous PTFE, porous urethane, porous polystyrene,porous silicone, porous fluoropolymer, porous polyolefin or acombination thereof. Porous polyolefin may, for example, be in the formof porous polyethylene, porous polypropylene, or a combination thereof.Porous polyethylene, porous polypropylene, and porous PTFE may beopen-celled. Porous urethane, porous silicone, porous fluoropolymer, andporous polystyrene may be close-celled. In an embodiment, the individualfibers may be composed of a single type of porous polymer. In anembodiment comprising porous PTFE, the porous PTFE may, for example,have a microstructure similar to as described in U.S. Pat. No. 4,187,390to Gore, the entirety of which is hereby incorporated by reference. Inan embodiment comprising porous PTFE, the porous PTFE may, for example,have a microstructure similar to as described in U.S. Pat. No. 5,476,598to Bacino, the entirety of which is hereby incorporated by reference.

The porosity may affect the acoustic attenuation properties of theporous polymer. For example, as the porosity is increased, the amount ofcaptured air, which is a poor conductor of acoustic energy, may alsoincrease, resulting in an aggregate material with exceptional acousticattenuation properties. Porous polymers may be operable to attenuateacoustic energy having a frequency between 100 kHz and 100 MHz. Forexample, porous PTFE may have acoustic attenuation capabilities greaterthan 50 dB/cm at 1 MHz. In fact, porous PTFE may have acousticattenuation capabilities greater than 10,000 dB/cm at 1 MHz. Bycomparison, silicone RTV may have an acoustic attenuation of less than 5dB/cm at 1 MHz.

FIG. 4 is a cross sectional view of the woven layer 200 in the sameorientation as illustrated in FIG. 3 with a filler material 401 disposedwithin the void space between fibers. As illustrated in FIG. 4, thefiller material 401 may fill the void space between individual fibersand also encapsulate the fibers. In such a configuration, the fillermaterial 401 may perform several functions.

One such function may be to provide mechanical support for the porousfibers of the woven layer 200. In this regard, the filler material 401may provide mechanical support for the woven layer 200 resulting in anencapsulated woven layer 400 that possesses a higher crush resistancethan the woven layer 200 alone.

The filler material 401 may also encapsulate the air or other gassestrapped within the porosity of individual fibers of the woven layer 200.In this regard, the filler material 401 may surround and seal theindividual fibers so that the air or other gasses trapped within theindividual fibers cannot escape to the surrounding areas. Similarly,gasses or liquids outside of the encapsulated woven layer 400 may beprevented from entering the pores of the individual fibers of the wovenlayer 200.

In embodiments where the polymer is an open-celled polymer, the fillermaterial 401 may surround the individual fibers of the woven layer 200without significantly penetrating into the fibers. Alternatively, thefiller material 401 may partially imbibe (e.g., partially soak into) theindividual fibers of the woven layer 200. Such partial imbibing mayresult in increased mechanical strength. The portions of the individualfibers of the woven layer 200 not filled with the filler material 401may contain, for example, entrained air. Accordingly, acousticattenuation properties associated with the interstitial spaces of theindividual fibers of the woven layer 200 may be retained after theindividual fibers of the woven layer 200 have been surrounded by thefiller material 401. With respect to open-celled polymers where partialimbibing is present, three distinct regions may be present. The firstregion may be the porous polymer where no filler material is present.The second region may be where the filler material has filled theinterstitial regions of the porous polymer. The third region may be alayer consisting of the filler material outside of the porous polymer.

In embodiments where the polymer is a close-celled polymer, the fillermaterial 401 may partially fill surface irregularities of the individualfibers of the woven layer 200. Such surface filling may promote bondingbetween the individual fibers of the woven layer 200 and the fillermaterial 401.

As will be appreciated, by varying such parameters as, for example, theporosity of the polymer used in the individual fibers, the size of theindividual fibers, the spacing between individual fibers within thewoven layer 200, the degree to which the filler material 401 imbibesinto the individual fibers (e.g., when the porous polymer isopen-celled), and the amount of filler material 401 used to encapsulatethe woven layer 200, various mechanical and acoustical properties of theencapsulated woven layer 400 may be achieved. In an embodiment, thefiller material 401 may be a thermoplastic and/or thermoset material.The filler material 401 may comprise THV, FEP, PTFE, PES, EFEP, PET,PEEK, PEI, PC, LCP, or a combination thereof. An exemplary thermoplasticmaterial is THV, such as Dyneon™ THV marketed by 3M, St. Paul. Minn.,U.S.A. In an exemplary embodiment including porous PTFE and THV, thecombination of PTFE and THV may have a benefit in that the acousticimpedance and acoustic propagation velocity of the two materials aresimilar enough not to cause significant reflections at the interfacebetween the two materials.

Turning to FIG. 5, an acoustic attenuation material member 500 maycomprise a first additional layer 501 and a second additional layer 502that may be interconnected to the encapsulated woven layer 400. In analternate embodiment, the acoustic attenuation material member 500 maycontain the single additional layer 501 but not the second additionallayer 502. The additional layers 501 and 502 may comprise a polymer witha predeterminable level of porosity. The additional layers 501 and 502may provide additional acoustic attenuation capabilities and provideadditional mechanical strength. An example of a material that comprisesa woven layer of porous PTFE fibers encapsulated in THV is Tenaramanufactured by W. L. Gore & Associates, Inc., Newark, Del., U.S.A.

FIG. 6 is a cross sectional view of an embodiment where two layers ofthe acoustic attenuation material member 500, as illustrated in FIG. 5,are bonded together with a layer of binding material 601. The layer ofbinding material 601 may be comprised of an adhesive polymer such as,for example, epoxy. In an exemplary implementation of the embodimentillustrated in FIG. 6, each of the acoustic attenuation material members500 comprised porous PTFE fibers (e.g., fiber 602) and porous PTFEadditional layers 603. The layer of bonding material 601 was less than0.025 mm in thickness and each of the acoustic attenuation materialmembers 500 was about 0.38 mm thick. Thicker layers of bonding materialmay be used, such as, for example, 0.05 mm.

In an embodiment of an acoustic attenuation material illustrated in FIG.7, two sheets 701, 702, each similar to the encapsulated woven layer 400of FIG. 4 and including an encapsulated layer of woven porous polymerfibers, may be bonded together with a bonding layer 703 (e.g., epoxy) toform an acoustic attenuation material 700 that remains flexible and hasparticular acoustic attenuation properties.

Materials as described that include at least one layer comprising awoven layer of polymer fibers with interstitial space may be used in avariety of acoustic attenuation applications. Such materials may be usedin ultrasound probes such as the above-described ultrasound probe ofFIG. 1. The materials may also be used in other acoustic attenuationapplications.

FIG. 8A is a cross-sectional view of an acoustic attenuation material800 that includes a plurality of porous-polymer sheets 801 (e.g.,membranes) interleaved with a plurality of sheets of support material802 (e.g., membranes and/or films). Such an acoustic attenuationmaterial 800 may be used, for example, for attenuating acoustic energy,including attenuating ultrasonic energy in ultrasound probes. The porouspolymer of the porous-polymer sheets 801 may be one or more of thepreviously discussed porous polymers. The porous polymer sheets may becomprised of a non-woven porous polymer. The sheets of support material802 may, for example, be comprised of a ceramic material, polymer,metal, or a combination thereof. In embodiments where the sheets ofsupport material 802 comprise polymer, the polymer may be a thermoset ora thermoplastic. For example, the polymer may be epoxy or fluoropolymer.

The sheets of support material 802 may be more rigid than theporous-polymer sheets 801. In this regard, in the acoustic attenuationmaterial 800, the porous-polymer sheets 801 may provide substantialacoustic attenuation and the sheets of support material 802 may providefor greater rigidity than would be achievable with the porous-polymersheets 801 alone. In this regard, the support material 802 may have agreater resistance to crushing and a greater flexural modulus than theporous-polymer sheets 801. For example, the flexural modulus of thesupport material 802 may be at least twice that of the porous-polymersheets 801. Also for example, the flexural modulus of the porous-polymersheets 801 may be less than 20 MPa while the net flexural modulus ofacoustic attenuation material 800 may be greater than 40 MPa.

The individual sheets of the acoustic attenuation material 800 may beindividually constructed and then laminated together to form theacoustic attenuation material 800. The layers of the laminated structuremay be bonded together using an adhesive. The layers of the laminatedstructure may be bonded together by processing the laminate so that someimbibing of the sheets of support material 802 into the porous-polymersheets 801 occurs.

The layers of the laminated structure may be bonded together usinglayers of adhesive disposed on a carrier. The adhesive may be pressuresensitive, such as for example, acrylic based pressure sensitiveadhesive. For example, a thin layer of double-sided tape 803 may bedisposed between adjacent layers of porous-polymer sheets 801 andsupport material 802. Other methods of laminating sheets known to thoseskilled in the art may be employed.

The thicknesses of the sheets of support material 802 and theporous-polymer sheets 801 may be varied to achieve various mechanicaland acoustic properties. For example, as shown in FIG. 8A, thethicknesses of the porous-polymer sheets 801 may be less than thethickness of the sheets of support material 802. In other embodiments,the sheets may be of equal thickness or the porous-polymer sheets 801may be thicker than the sheets of support material 802.

In an embodiment, each porous-polymer sheet 801 may have a thicknessless than 800 microns, and each sheet of support material 802 may have athickness less than 500 microns. For example, each porous-polymer sheet801 may have a thickness between 1 and 800 microns, and each sheet ofsupport material 802 may have a thickness between 1 and 500 microns. Ina particular exemplary embodiment, each porous-polymer sheet 801 may beabout 30 microns thick and each sheet of support material 802 may beabout 25 microns thick.

The acoustic attenuation material 800 illustrated in FIG. 8A shows aconfiguration where individual layers are in the same orientation as theoverall structure. FIG. 8B is a cross-sectional view of an acousticattenuation material 808 that includes a plurality of porous-polymersheets 804 interleaved with a plurality of sheets of a support material805. In the embodiment illustrated in FIG. 8B, the orientation of theindividual layers 804, 805 is oriented at an angle 807 with respect tothe orientation of the overall structure of the acoustic attenuationmaterial 808. The angle 807 may be varied to achieve various acousticand mechanical properties. Optional sealing layers 806 may be added tothe top and/or bottom of the acoustic attenuation material 808 toprevent exposure of the edges of the porous-polymer sheets 804 and/orsheets of support material 805 to the surrounding environment. Thequantity of layers present in the acoustic attenuation materials 800 and808 may be varied from that illustrated in FIGS. 8A and 8B.

The configuration of FIG. 8A is such that a sound beam traveling from afirst side 810 of the acoustic attenuation material 800 to a second sideof the acoustic attenuation material 811 must pass through a pluralityof layers of the porous-polymer sheets such as the porous-polymer sheets801. The angle 807 of the configuration of FIG. 8B, along with theorientation of the overall structure of the acoustic attenuationmaterial 808, may be chosen such that a sound beam traveling from afirst side 812 of the acoustic attenuation material 808 to a second side813 of the acoustic attenuation material 808 must pass through aplurality of layers of the porous-polymer sheets such as porous-polymersheet 804.

Materials as described with reference to FIGS. 8A and 8B that include aplurality of porous-polymer sheets interleaved with a plurality ofsheets of support material may be used in a variety of acousticattenuation applications. Such materials may possess a net acousticattenuation of at least 25 dB/cm at 1 MHz and may be operable toattenuate acoustic energy having a frequency between 100 kHz and 100MHz. Such materials may be used in ultrasound probes such as theabove-described ultrasound probe of FIG. 1. The materials may also beused in other acoustic attenuation applications.

FIG. 9 is an isometric view of a section of an acoustic attenuationmaterial that includes a sheet 900 comprised of a porous polymercomprising multiple through holes, such as through hole 901. In anexemplary embodiment, the sheet 900 may be between 1 and 200 micronsthick. The porous polymer of the sheet 900 may be one or more of thepreviously discussed polymers. In an embodiment, the sheet 900 may beconstructed of porous PTFE, and/or other porous polymers (e.g.,urethane, silicone, fluoropolymer, polystyrene and polyolefin). Thesheet 900 may be comprised of a non-woven porous polymer.

The sizes of the holes (e.g., the area or diameter of the holes), thenumber of holes, and the pattern of holes may all be varied to achieveparticular material properties as discussed below. FIG. 10 is a crosssectional view of the sheet 900 of FIG. 9 along section line B-B, Theholes may be created by any appropriate means known to those skilled inthe art, including for example, laser drilling. The holes may beuniformly or non-uniformly distributed. The holes may all be the samesize or the sizes of individual holes may vary.

FIG. 11 is a cross sectional view of an embodiment of a rigid compositematerial 1100. The rigid composite material 1100 includes a plurality oflayers of porous-polymer sheets such as the sheet 900 of acousticattenuation material and an additional sheet 1101 of acousticattenuation material. The additional sheet 1101 may be constructed ofthe same material and may also have the same through holecharacteristics as the sheet 900. As illustrated in FIG. 11, theporous-polymer sheets may be interleaved with layers of a supportmaterial 1102. The layers of support material 1102 may also occupy atleast a portion of the through holes of the porous-polymer sheets 900,1101. In this regard, the layers of support material 1102 may form athree-dimensionally interconnected rigid matrix. The thickness of thelayers of support material 1102 between the porous-polymer sheets 900,1101 may, for example, be between 1 and 200 microns thick.

The combination of layers of support material 1102 interleaved withlayers of acoustic attenuation material provides for a compositematerial 1100 that possesses exceptional acoustic attenuation andmechanical properties. In this regard, the layers of support material1102, which may, for example, comprise epoxy, THV, FEP, PES, EFEP, PTFE,PET, PEEK, PEI, PC, LCP or a combination thereof, may have a greaterresistance to crushing and a greater flexural modulus than theporous-polymer sheets 900, 1101. For example, the flexural modulus ofthe layers of support material 1102 may be at least twice that of theporous-polymer sheets 900, 1101. Also for example, the flexural modulusof the porous-polymer sheets 900, 1101 may be less than 20 MPa while thenet flexural modulus of composite material 1100 may be greater than 40MPa.

Thus, the composite material 1100 may gain mechanical strength from thelayers of support material 1102 while gaining acoustic attenuationproperties from the porous-polymer sheets 900, 1101. The compositematerial may possess a net acoustic attenuation of at least 25 dB/cm at1 MHz and may be operable to attenuate acoustic energy having afrequency between 100 kHz and 100 MHz.

The mechanical and acoustical properties of the composite material 1100may be varied by varying the thicknesses of the different layers and theconfigurations of the holes in the porous-polymer sheets. For example,as shown in FIG. 11, the holes in the two sheets 900, 1101 are notaligned. In general, the porous-polymer sheets 900, 1101 will have asignificantly higher rate of acoustic attenuation than the layers ofsupport material 1102. Accordingly, acoustic energy passing through therigid composite material 1100 will be transmitted primarily through thestructure of the layers of support material 1102. By staggering theholes of the porous-polymer sheets 900, 1101, the acoustic energytraveling through the layers of support material 1102 is forced tofollow a serpentine path. In this regard, any sound beam traveling froma top surface 1103, through the composite material 1100 to a bottomsurface 1104, must pass through at least a portion of the porous-polymersheets 900, 1101. This will tend to attenuate the acoustic energy to agreater degree than what would occur if the holes of the porous-polymersheets 900, 1101 were in a line and the acoustic energy travelingthrough the layers of support material 1102 were able to follow astraight-line path through the composite material 1100.

Similar to the alignment of the holes of the porous-polymer sheets, thesize and quantity of holes may be varied to balance desired acousticattenuation properties and desired mechanical properties. For example,in general larger through holes may result in a more rigid and strongercomposite material 1100. Larger through holes or increased number ofthrough holes may also result in a larger pathway for acoustic energy totravel through the rigid composite material 1100, which may result in amore rigid, stronger composite material 1100 with lower overall acousticattenuation.

Additionally, and similar to as discussed above, some imbibing of theepoxy into the layers of porous-polymer may occur where open-celledpolymer is used. Substantially no imbibing may occur where the pore sizeof an open-celled polymer is below a predetermined amount or where aclose-celled polymer is used. Where imbibing does occur, it may have asimilar effect as reducing the thickness of the porous-polymer layersand/or increasing the size of the through holes of the porous-polymerlayers 900, 1101.

Moreover, in general, regions where support material has imbibed into aportion of the porosity of a porous-polymer layer may be significantlystiffer then regions of the porous-polymer layer free of the supportmaterial. For example, a region where support material has imbibed intoa portion of the porosity of a porous-polymer layer may have a flexuralmodulus greater than twice that of a region of the porous-polymer layerfree of support material.

The degree of imbibing may be affected by processing and handling. Forexample, in embodiments that include porous PTFE, wetting the porousPTFE with a solvent prior to contact with the layers of support material1102 during the manufacture of the composite material 1100 may increasethe degree of imbibing of the support material into the porous PTFE.Additionally, any compressive forces applied to the composite material1100 during or after manufacture may cause the layers of supportmaterial 1102 to imbibe into the porous-polymer layers 900, 1101.Compressive forces on the composite material 1100 may also crush (e.g.,permanently compress) the porous-polymer layers 900, 1101.

The composite material 1100 illustrated in FIG. 11 includes twoporous-polymer layers 900, 1101. Other embodiments may include a singleporous-polymer layer or more than two porous-polymer layers. Forexample, an embodiment of an acoustic attenuation material wasconstructed using three porous-PTFE layers interleaved with layers ofepoxy. A plurality of holes averaging about 0.14 mm in diameter andencompassing about 10.7 percent of the total surface area of theporous-PTFE layers were drilled into each of the PTFE layers. In onesample, the holes of the individual porous-PTFE layers were arrangedwith a high degree of alignment. The acoustic attenuation of that samplewas measured to be 375 dB/cm at 1 MHz. In another sample, the holes ofthe individual porous-PTFE layers were arranged with a relatively lowdegree of alignment. The acoustic attenuation of the low degree ofalignment sample was measured to be 431 dB/cm at 1 MHz.

Another embodiment was constructed using two porous-PTFE layersinterleaved with layers of epoxy. The porous-PTFE layers included aplurality of holes. The embodiment showed no plastic deformation whencompressed at 50 psi. A similar embodiment without the plurality ofholes in the porous-PTFE layers may show plastic deformation of about 3percent when compressed at 50 psi.

Blind holes may be substituted for the through holes described above,such as through hole 901. Such a configuration eliminates a continuoussupport material acoustic path through the composite material 1100.

Materials as described that include at least one sheet of a porouspolymer that includes holes (e.g., through holes) may be used in avariety of acoustic attenuation applications. Such materials may be usedin ultrasound probes such as the above-described ultrasound probe ofFIG. 1. The materials may also be used in other acoustic attenuationapplications. Indeed, such materials may be used in a wide variety ofapplications where it is desired to attenuate acoustic energy.

Each of the acoustic attenuation materials described above may beproduced in master sheets that are larger than the size needed for aparticular application. For example, a master sheet of acousticattenuation material may be produced for use as backing material inultrasonic transducers that includes enough material for a plurality ofindividual ultrasonic transducer systems. The master sheet may, forexample, be separated into individual sections for use in individualultrasonic transducer systems. The process may also include a step whereexposed edges of the individual sections are sealed with a sealingmaterial (e.g., epoxy and/or thermoplastic fluoropolymer).

In embodiments where individual sections of acoustic attenuationmaterial are manufactured (e.g., where no master sheets are produced),the process may include a step where exposed edges of acousticattenuation material are sealed with a sealing material (e.g., epoxyand/or thermoplastic fluoropolymer).

In each of the acoustic attenuation materials described above, theporous polymer may have significantly greater acoustic attenuationcapabilities than the material used to provide support. For example, theacoustic attenuation capabilities of the porous polymer may be more thantwice that of the support material. Additionally, the support materialmay be significantly more rigid (e.g., possess a greater stiffness) thanthe porous polymer. For example, the support material may have aflexural modulus twice that of the porous polymer. Moreover, the porouspolymer may have a porosity of at least 5 percent. For example, theporous polymer may have a porosity of between 5 and 85 percent.

The above-described materials may, for example, be utilized in systemswhere it is desired to control acoustic energy. Additionally, due to therelatively high attenuation per unit thickness of the above-describedmaterials, greater attenuation can be achieved for a particularthickness of attenuation material or alternatively, a desired amount ofattenuation can be used with relatively less attenuation material. Thelatter capability is particularly advantageous in applications whereminiaturization is desired. In particular, ultrasound probes, an exampleof which was previously discussed with reference to FIG. 1, generallyutilize acoustic attenuation material to control the acoustic energygenerated by one or more active (e.g., piezoelectric) elements. The useof the above-described materials in ultrasonic transducers may, forexample, enable better performing probes of the same size as currentprobes and/or smaller transducer probes.

FIG. 12 illustrates a perspective view of an ultrasound probe assembly1200. The probe assembly 1200 includes a housing 1201 and a cable 1202.The cable 1202 is interconnected to an ultrasound imaging apparatus (notshown). Generally, the probe assembly 1200 includes a plurality ofultrasonic transducers contained within the housing 1201 and operable totransmit ultrasonic energy through a probe assembly face 1203 along oneend of the probe assembly 1200. The ultrasonic energy, in the form ofacoustic waves, may be directed through the outer surface of a patientand into the internal structure of the patient. The acoustic waves mayinteract with and reflect off of various internal features. Thesereflections may then be detected by the probe assembly 1200 anddisplayed as images of the internal structure of the patient by theultrasound imaging apparatus.

The probe assembly 1200 may be operable to scan an imaging volume 1208.This may be accomplished by mounting a one-dimensional transducer arrayon a movable member. Generally, one-dimensional transducer arraysinclude a single row containing a plurality of transducer elements alonga longitudinal axis 1205. Through electronic control, a beam of acousticenergy may be swept along the longitudinal axis 1205. Some of theacoustic energy is reflected back to the transducer array where it isconverted by the transducer array from acoustic energy to electricalsignals. These electrical signals may then be converted into atwo-dimensional image of the area swept by the acoustic energy. Theprobe assembly 1200 may contain a one-dimensional transducer array thatmay be mechanically swept (e.g., rotated) along an elevation axis 1204.Thus, through a combination of electronic sweeping along a longitudinalaxis 1205 and mechanical sweeping of the transducer array along anelevation axis 1204, a beam of acoustic energy may be swept through theimaging volume 1208. Energy reflected back to the transducer array maybe converted into a three-dimensional image of the imaging volume 1208.

The transducer array in probe assembly 1200 may be a two-dimensionalarray that may be mechanically swept (e.g., rotated) along an elevationaxis 1204. The dimension of the array perpendicular to the axis ofrotation (e.g., the elevation axis 1204) may be utilized to furthercontrol the transmitted acoustic energy. For example, transducers alongthe elevation axis 1204 may be used to shape the acoustic energy toreduce side lobes and improve focus along the elevation axis 1204.

Turning to FIG. 13, a cross-sectional schematic view of aone-dimensional ultrasonic transducer system 1300 is presented. Theultrasonic transducer system 1300 has a longitudinal axis 1305 and anelevation axis 1304, which, for example, are similar to the longitudinalaxis 1205 and elevation axis 1204, respectively, of the probe assemblyof FIG. 12. The ultrasonic transducer system 1300 may be operable totransmit and/or receive ultrasonic signals.

Generally, as known to those skilled in the art, a transducer 1315(comprising an active layer such as piezoelectric layer 1306 and anyoptional matching layer attached thereto described below) may be dividedinto a predetermined number of discrete sections (for example, sections1309 a through 1309 n, where n represents the predetermined number ofdiscreet sections) along the longitudinal axis 1305. Each of thesediscrete sections may be a transducer element (e.g., discrete section1309 a may be a transducer element). The discrete sections may beelectrically interconnected so that two or more of the discrete sectionsoperate as a single transducer element (e.g., discrete sections 1309 aand 1309 b may be electrically interconnected and function as a singletransducer element). A backing 1313 may also be present.

FIG. 13 shows the ultrasonic transducer system 1300 as being straightalong the longitudinal axis 1305. The ultrasonic transducer system 1300may be curved along the longitudinal axis 1305. This curvature may, forexample, be achieved by placing individual planar transducer elements atangles to each other along the longitudinal axis 1305. FIG. 13 alsoshows the individual transducer elements of the ultrasonic transducersystem 1300 as planar along the elevation axis 1304. In an alternativeconfiguration, the individual transducer elements of the ultrasonictransducer system 1300 may be curved along the elevation axis 1304.

The transducer 1315 may include a piezoelectric layer 1306. Thepiezoelectric layer 1306 may include a layer of piezoelectric material1320, a first electrode layer 1321 and a second electrode layer 1322.The layer of piezoelectric material 1320 may be comprised of aceramic-based material (e.g., lead zirconate titanate (PZT)). The firstelectrode layer 1321 may be comprised of one or more layers ofelectrically conductive material. Similarly, the second electrode layer1322 may be comprised of one or more layers of electrically conductivematerial. The portion of the first electrode layer 1321 connected toeach individual transducer element may serve as the signal electrode forthat individual transducer element. Similarly, the portion of the secondelectrode layer 1322 connected to each individual transducer element mayserve as the ground electrode for that individual transducer element.

Generally, the signal electrodes and ground electrodes are arranged asillustrated in FIG. 13 with the ground electrode on the side of thepiezoelectric material 1320 that faces the region to be imaged. Theposition of the signal and ground electrodes may be reversed. In suchembodiments, it may be necessary to provide an additional groundinglayer to shield the signal layer. The ground electrodes may beindividual electrodes as illustrated in FIG. 13 or may be one continuouslayer of grounding material situated over each of the individualtransducer elements. The individual transducer element electrodes may beinterconnected to electronic circuitry, which may provide for acousticwave generation and sensing.

Optional acoustic matching layers may be interconnected to thepiezoelectric layer 1306. The ultrasonic transducer system 1300 of FIG.13 shows a first optional matching layer 1307 and a second optionalmatching layer 1308 interconnected to the piezoelectric layer 1306. Thepresence and number of optional matching layers may vary from theconfiguration illustrated in FIG. 13. The transducer 1315 comprises thepiezoelectric layer 1306, along with any optional matching layersattached thereto.

The piezoelectric layer 1306 may be a mechanically active layer operableto convert electrical energy to mechanical energy and mechanical energyinto electrical energy. As previously described, the piezoelectric layer1306 may be comprised of a layer of PZT material sandwiched betweenground and signal electrodes. A variety of components and materials ableto generate acoustic signals may be substituted for at least a portionof the piezoelectric layer 1306. Such components and materials includeceramic materials, ferroelectric materials, composite materials,capacitor micromachined ultrasound transducers (CMUTs), piezoelectricmicromachined ultrasound transducers (PMUTs), and any combinationthereof. Regardless of the specific components, electromechanicalprinciple of operation or materials, the mechanically active layer maycomprise a means of converting electrical energy to mechanical energyand mechanical energy into electrical energy, which has an acoustic face1314 and a plurality of transducer elements that may be controlledindividually. Generally, any system known to those skilled in the artfor generating ultrasonic acoustic signals that may be used for imagingpurposes may be utilized in the mechanically active layer.

Returning to FIG. 13, each individual discrete section may be separatedfrom neighboring discrete sections by kerfs (e.g., kerf 1310 betweendiscrete sections 1309 c and 1309 d) produced during the dicing of thetransducer 1315. The kerfs may be filled with a filler material.Additionally, one or more acoustic lenses may be interconnected to theacoustic face 1314.

As the piezoelectric layer 1306 emits acoustic energy, some acousticenergy will pass into the backing 1313. Since such acoustic energy isnot directed to the imaging volume 1208, it is desirable that thisacoustic energy be attenuated. Attenuating this acoustic energy helps toreduce the amount of acoustic energy being reflected back into thepiezoelectric layer 1306 through the back side of the piezoelectriclayer 1306. Such reflected acoustic energy may interfere with theacoustic energy being reflected back to the piezoelectric 1306 from theimaging volume 1208, which may result in image degradation.

The backing 1313 may include an intermediate layer 1301. Theintermediate layer 1301 may be comprised of material or materials knownto those skilled in the art of ultrasonic transducer design, such as,for example epoxy, silicone rubber, tungsten, aluminum oxide, mica,microspheres, or a combination thereof. The backing 1313 may alsoinclude a second layer 1302. The second layer 1302 may be a highlyattenuating material such as the materials previously described thatinclude a woven layer of fibers made of porous-polymers (e.g., thefibers may be made of porous-PTFE). By way of example, the second layer1302 may be composed of the acoustic attenuation materials describedwith respect to FIGS. 6 and/or 7.

FIG. 14 is an illustration of a transducer and frame assembly 1400. Thetransducer and frame assembly 1400 includes the ultrasonic transducersystem 1300 of FIG. 13 mounted to a frame 1401. As described above withrespect to FIG. 13, the ultrasonic transducer system 1300 may includethe transducer array 1315, the intermediate layer 1301, and the secondlayer 1302. The transducer and frame assembly 1400 may, for example, bemounted within the probe assembly 1200 of FIG. 12. The transducer andframe assembly 1400 may be mounted so that it is rotatable about a framerotation axis 1402. In such a system, and as previously described, anacoustic beam may be electronically steered along a longitudinal axis1405 and mechanically steered by rotating the transducer and frameassembly 1400 about the frame rotation axis 1402. A motor or otherdevice (not shown) may be used to rotate the transducer and frameassembly 1400 about the frame rotation axis 1402.

To acoustically couple the transducer array 1300 to the probe assemblyface 1203 of FIG. 12, the transducer and frame assembly 1400 may beimmersed in a fluid (e.g., a liquid). The fluid may be contained withinthe housing 1201 of the probe assembly 1200 of FIG. 12.

As noted above, the transducer and frame assembly 1400 may be rotatedwithin the housing 1201 in order to achieve scanning of an acoustic beamalong an elevation axis 1204. Furthermore, and as noted above, thetransducer and frame assembly 1400 may be immersed in a liquid. In sucha system, it may be beneficial to reduce the size and/or weight of thetransducer and frame assembly 1400. By reducing the size of thetransducer and frame assembly 1400, the resistance to movement of thetransducer and frame assembly 1400 due to the fluid in which it isimmersed may be reduced. By reducing the weight of the transducer andframe assembly 1400, the inertia of the transducer and frame assembly1400 may be reduced. Reducing the resistance to movement and/or theinertia of the transducer frame assembly 1400 may yield, inter alia,increased positional accuracy, lower movement response time, and reducedmotor power requirements.

Accordingly, the use of a backing that incorporates at least one wovenlayer of porous-polymer fibers, as described above, in place oftraditional ultrasonic transducer backing material (e.g., siliconerubber) may provide weight and size reduction benefits. Similarly, if atraditional ultrasonic transducer backing material is replaced with asimilarly sized backing that incorporates at least one woven layer ofporous-polymer fibers, the acoustic attenuation of the backing may beenhanced.

Additionally, the flexibility of the above-described woven layers ofporous-polymer fibers permits curved transducer arrays, such as thetransducer array 1300 of FIG. 14, to be manufactured efficiently. Forexample, the transducer array 1300 of FIG. 14 may be initiallymanufactured as a flat transducer array. In this regard, a flatcontinuous layer of piezoelectric material may be interconnected to abacking that includes at least one woven layer of the porous polymerfibers. After the piezoelectric material is diced to form individualtransducer array elements, this assembly may be interconnected to acurved surface, such as the curved surface 1403 of the frame 1401 of thetransducer and frame assembly 1400. The kerfs produced as a result ofthe dicing process may then be filled.

Returning to FIG. 13, the first electrode layer 1321 and the secondelectrode layer 1322 may be electrically interconnected to theultrasound imaging apparatus in a variety of ways. For example, theelectrical interconnections to the first electrode layer 1321 of eachindividual transducer element (e.g., discrete sections 1309 a through1309 n) may be achieved by electrically interconnecting to the firstelectrode layer 1321 along an the edge of the transducer 1315. Forexample, the first electrode layer 1321 of discrete section 1309 c maybe interconnected to at the exposed end 1303 of discrete section 1309 c.

FIG. 15 illustrates another method of electrically interconnecting theultrasound imaging apparatus to the first electrode layer 1321 of thediscrete sections of the transducer 1315. FIG. 15 is a cross-sectionalview of the ultrasonic transducer system 1300 of FIG. 13 along sectionline C-C of FIG. 13 with the addition of a plurality of electricalinterconnections 1501 a through 1501 n. Each of the plurality ofelectrical interconnections 1501 a through 1501 n extends through theintermediate layer 1301 and the second layer 1302. For example,electrical interconnection 1501 a is electrically interconnected to thefirst electrode layer 1321 of discrete section 1309 a and extendsthrough the intermediate layer 1301 and the second layer 1302. Exposedportion 1503 of electrical interconnection 1501 a is electricallyinterconnected to the first electrode layer 1321 of discrete section1309 a. The exposed portion 1503 may be electrically interconnected tothe ultrasound imaging apparatus using methods known to those skilled inthe art. Alternatively, electrical interconnections 1501 a through 1501n may not extend past the bottom surface 1504 of the second layer 1302.In such a configuration, the electrical interconnections 1501 a through1501 n may be interconnected to the ultrasound imaging apparatus usingmethods known to those skilled in the art such as, for example,wirebonding.

The electrical interconnections 1501 a through 1501 n may be formed byfirst creating holes through the intermediate layer 1301 and the secondlayer 1302. This may be accomplished, for example, by laser drilling.The holes may then be filled with an electrically conductive material(e.g., by a plating process). The electrical interconnections 1501 athrough 1501 n may be configured such that a single electricalconnection may be electrically interconnected to a plurality of discretesection. For example, electrical interconnection 1501 a may beelectrically interconnected to discrete sections 1309 a and 1309 b. Insuch a configuration, discrete sections 1309 a and 1309 b together mayform a single transducer element and electrical interconnection 1501 bmay not be present. The electrical interconnections 1501 a through 1501n may be oriented transverse to discrete sections to which they areelectrically interconnected.

FIG. 16 illustrates another method of electrically interconnecting theultrasound imaging apparatus to the first electrode layer 1321 of thediscrete sections of the transducer 1315. FIG. 16 is a schematic diagramof a backing assembly 1600 for use in an ultrasonic transducer assembly.To avoid repetition, the transducer array is not illustrated in FIG. 16.Rather, only the backing assembly 1600 is shown. The backing assembly1600 is illustrated in a similar orientation to the ultrasonictransducer system 1300 of FIG. 13.

The backing assembly 1600 of FIG. 16 includes an intermediate layer 1601and a second layer 1602. Similar to as discussed above with respect tothe ultrasonic transducer system 1300, the intermediate layer 1601 maybe composed of a material or materials known to those skilled in the artof ultrasonic transducer design and the second layer 1602 may be ahighly attenuating material such as the materials previously describedthat include a woven layer of fibers made of porous polymers. Thebacking assembly 1600 includes an interconnection assembly 1603. Theinterconnection assembly 1603 may be comprised of an insulating material1604 and individual electrical conduction members. The interconnectionassembly 1603 may be disposed between sections of the intermediate layer1601 and the second layer 1602 as illustrated in FIG. 16. A sectionalong lines 1607 has been cut away in FIG. 16 to reveal internal detailsof the interconnection assembly 1603.

The individual electrical conduction members may be individual wires,such as wire 1605. The individual wires may be disposed in slots, suchas slot 1606, within the insulating material and oriented transverse tothe individual transducer elements. In this regard, the interconnectionassembly 1603 may be comprised of a plurality of electricalinterconnections passing through the backing assembly 1600. Theinsulating material 1604 may be composed of the same material as theintermediate layer 1601.

As noted above in reference to FIG. 1, acoustic attenuation material 114may be placed along other surfaces within the ultrasound probe 100.Similarly in embodiments such as that illustrated in FIG. 12, theabove-described acoustic attenuation materials may be used to line thehousing 1201 and/or other components within the probe assembly 1200.Such application of the above-described acoustic attenuation materialsmay help to improve image quality by reducing the amount of unwantedacoustic energy incident upon an ultrasonic transducer array, such astransducer array 1300 of FIG. 13. Generally, the above-describedacoustic attenuation materials may be positioned against a surface wherea front side of the acoustic attenuation material is in a face-to-facerelationship with the surface and a back side of the acousticattenuation material is in contact with a fluid (e.g., air or water). Insuch a position, the acoustic attenuation material may be operable toabsorb acoustic energy emanating from the surface and acoustic energytraveling through the fluid and incident upon the back side of theacoustic attenuation material.

Turning to FIG. 17, a cross-sectional schematic view of an ultrasonictransducer system 1700 is presented. A section along lines 1711 and 1712has been cutaway in FIG. 17 to reveal internal details of the ultrasonictransducer system 1700. The ultrasonic transducer system 1700 has alongitudinal axis 1705 and an elevation axis 1704. The ultrasonictransducer system 1700 is comprised of a predetermined number ofdiscrete sections represented in FIG. 17 by discrete sections 1709 athrough 1709 n, where n represents the predetermined number of discretesections. The ultrasonic transducer system 1700 is shown as aone-dimensional array with a single row of n transducers, where nrepresents a predetermined number of discrete sections. Alternatively,the ultrasonic transducer system 1700 may comprise a two-dimensionalarray of discrete section arranged in multiple rows and multiplecolumns.

Generally, as is known to those skilled in the art, a transducer 1715(comprising of a piezoelectric layer 1706 and any optional matchinglayer attached thereto) may be divided into a predetermined number ofdiscrete sections represented in FIG. 17 by discrete sections 1709 athrough 1709 n arranged along the longitudinal axis 1705. Similarly toas discussed with reference to FIG. 13, these discrete sections may eachform a transducer element or they may be electrically combined so thattwo or more discrete sections may form a transducer element. A backing1701, described below, may also be present.

The transducer 1715 may include a piezoelectric layer 1706. Thepiezoelectric layer 1706 may include a layer of piezoelectric material1720, a first electrode layer 1721 and a second electrode layer 1722.The layer of piezoelectric material 1720 may be comprised of aceramic-based material. The first electrode layer 1721 may be comprisedof one or more layers of electrically conductive material. Similarly,the second electrode layer 1722 may be comprised of one or more layersof electrically conductive material. The portion of the first electrodelayer 1721 connected to each individual transducer element may serve asthe signal electrode for that individual transducer element. Similarly,the second electrode layer 1722 may serve as the ground electrode. Theindividual transducer element electrodes may be interconnected toelectronic circuitry, which may provide for acoustic wave generation andsensing. Optional acoustic matching layers may be interconnected to thepiezoelectric layer 1706.

The ultrasonic transducer system 1700 of FIG. 17 shows a single optionalmatching layer 1707. The presence and number of optional matching layersmay vary from the configuration illustrated in FIG. 17. The transducer1715 comprises the piezoelectric layer 1706, along with any optionalmatching layers attached thereto.

The piezoelectric layer 1706 may be a mechanically active layer operableto convert electrical energy to mechanical energy and mechanical energyinto electrical energy and may be comprised of any of the materialsdiscussed above with reference to the piezoelectric layer 1306 of FIG.13. The transducer 1715 of FIG. 17 includes an acoustic face 1714. Eachindividual transducer element may be separated from neighboring elementsby kerfs (e.g., kerf 1710 between discrete sections 1709 c and 1709 d)produced during the dicing of the transducer 1715.

The backing 1701 of the ultrasonic transducer system 1700 may comprisethe composite material described above with reference to FIG. 11. Inthis regard, the backing 1701 may include one or more porous-polymersheets, such as sheets 1703 a, 1703 b and 1703 c interleaved with layersof a support material 1702. The support material may, for example, becomprised of an epoxy. Each of the porous-polymer sheets 1703 a, 1703 band 1703 c may be composed of porous PTFE. Each of the porous-polymersheets 1703 a, 1703 b and 1703 c may include a plurality of throughholes, such as through hole 1708. The plurality of through holes may beat least partially filled with the support material 1702.

FIG. 17 illustrates a backing 1701 containing three layers ofporous-polymer sheets 1703 a, 1703 b and 1703 c. Various embodiments mayuse a single porous-polymer sheet, two porous-polymer sheets, or four ormore porous-polymer sheets. Hole patterns in the porous-polymer sheetsmay vary from that illustrated in FIG. 17. The hole size, quantity andpattern may be varied to achieve desired mechanical and/or acousticproperties.

As shown in FIG. 17, the support material 1702 completely encapsulatesthe porous-polymer sheets 1703 a, 1703 b and 1703 c. Such aconfiguration may be achieved by precutting the individualporous-polymer sheets 1703 a, 1703 b and 1703 c and then encapsulatingthem within the support material 1702.

Alternatively, the backing 1701 may be produced in sizes larger thanwhat would be required for a single ultrasonic transducer system 1700.For example, a sheet of backing material several times larger than thatrequired for a single ultrasonic transducer system 1700 may be provided.A similarly sized layer of piezoelectric material may be interconnectedto the sheet of backing material along with any optional matching layersthat may be desired. This assembly may then be diced to produce kerfsbetween strips of piezoelectric material. The kerfs may then be filled.The entire assembly could then be cut into individual ultrasonictransducer systems such as the ultrasonic transducer system 1700 of FIG.17.

In this regard, the backing 1701 may be reduced to its final size (e.g.,by slicing) with the edges of the individual porous-polymer sheets 1703a, 1703 b and 1703 c exposed along the sides of the backing 1701.Depending on the application and working environment of the ultrasonictransducer system 1700, the edges of the individual porous-polymersheets 1703 a, 1703 b and 1703 c may remain exposed or the edges may besealed in a manufacturing step (e.g., by placing a layer of epoxy aroundthe edges of the backing 1701). The edges may be sealed to, for example,prevent substances from entering the pores of the porous-polymer sheetsor to provide additional mechanical integrity.

Electrical interconnection to the individual transducer elements of theultrasonic transducer system 1700 may be achieved in manner similar toas discussed above with respect to the ultrasonic transducer system 1300of FIG. 13. For example, the electrical interconnections to the firstelectrode layer 1721 of each individual transducer element may beachieved by electrically interconnecting to the first electrode layer1721 along an the edge of the transducer 1715. For example, theelectrical interconnections to the first electrode layer 1721 may beachieved by electrically connecting through the backing 1701 in a mannersimilar to that described above with reference to FIG. 15 (e.g.,drilling through the backing 1701 and plating) and FIG. 16 (e.g., usingan interconnection assembly similar to the interconnection assembly1603).

Once situated in, for example, an ultrasound probe, the ultrasonictransducer system 1700 may be oriented such that the acoustic face 1714is in proximity to an outer portion of the ultrasound probe.Accordingly, the rear of the ultrasonic transducer system 1700 (e.g.,the rear face of the backing 1701 opposite from the piezoelectric layer1706) may face away from the outer portion of the ultrasound probe andtoward an internal portion of the ultrasound probe. In this regard, therear face of the backing 1701 may be exposed to an internal environmentof the ultrasound probe that may, for example, contain air.

FIG. 17 shows the ultrasonic transducer system 1700 as being straightalong the elevation axis 1704. In an alternate configuration, theindividual transducer elements of the ultrasonic transducer system 1700may be curved along the elevation axis 1704.

FIG. 17 illustrates the ultrasonic transducer system 1700 with a backing1701 similar to the material described with reference to FIGS. 9-11. Itis noted that the ultrasonic transducer system 1700 may also beconfigured using the backing materials described with reference to FIGS.8A and 8B.

FIGS. 18 and 19 illustrate an exemplary application of the ultrasonictransducer system 1700 of FIG. 17. FIG. 18 illustrates a catheter 1800that contains an ultrasonic transducer. The catheter 1800 comprises anouter shell 1801 surrounding an ultrasonic transducer and aninterconnected tube 1802. The tube 1802 may contain electricallyconductive pathways to electrically interconnect the ultrasonictransducer with an ultrasound imaging apparatus (not shown). Theultrasonic transducer within the catheter 1800 may be oriented along alongitudinal axis 1805 and an elevation axis 1804 so that a beam ofacoustic energy may be swept through an imaging plane 1808.

The ultrasonic energy, in the form of acoustic waves, may be directedinto the internal structure of a patient. The acoustic waves mayinteract with and reflect off of various internal features. Thesereflections may then be detected by ultrasonic transducer within thecatheter 1800 and displayed as images of the internal structure of thepatient by the ultrasound imaging apparatus.

FIG. 19 is a cross sectional view along section line D-D of the catheter1800 of FIG. 18. The ultrasonic transducer system 1700, comprising thetransducer 1715 and the backing 1701, is disposed within the outer shell1801. The catheter 1800 also includes an electrical interconnectionassembly 1904 that electrically interconnects to the ultrasonictransducer system 1700. The electrical interconnection assembly 1904may, for example, be a GORE™ MicroFlat Ribbon Cable available from W. L.Gore & Associates, Inc., Newark, Del., U.S.A. The catheter 1800 may alsoinclude a working channel 1905.

The backing 1701 may, for example, be constructed in accordance with theembodiments described with reference to FIGS. 8A through 11. It will beappreciated that since the backing 1701 may be comprised ofporous-polymer sheets that have a high attenuation per unit thickness(relative to traditional ultrasonic transducer backing materials), thebacking 1701 may be thinner than a backing of similar attenuationcapability made from traditional backing materials (e.g., epoxy,silicone rubber). The thinner, rigid backing 1701 has severaladvantages. For example, in a round catheter such as catheter 1800, asthe backing thickness is decreased, the maximum width of the ultrasonictransducer system 1700 may be increased. Also, as the backing thicknessis decreased, the room available for other components within thecatheter is increased and/or the overall size of the catheter may bedecreased. The rigidity of the backing 1701 also is operable to supportand/or position the transducer 1715 without the need for supplementalsupport members. Additionally, the above-described methods ofelectrically interconnecting to the transducer 1715 through the backing1701 may result in no need for electrical connections along the edges ofthe transducer 1715 and therefore the transducer 1715 and backing 1701may extend to, or close to, the outer shell 1801 of the catheter 1800.

The acoustic attenuation materials described herein may be used in awide variety of locations. As noted above, the acoustic attenuationmaterials may be used to line the interior of the housing 1201 of probeassembly 1200. FIG. 20 illustrates an exemplary embodiment whereacoustic attenuation material 2001 is interconnected (e.g., bonded withepoxy) to a support structure 2002 to form an acoustic energy-absorbingpanel 2000. Such a panel 2000 may be positioned in a wide variety oflocations to absorb acoustic energy. For example, the panel may besituated within a predetermined volume where it is desired to reduce thelevel of acoustic energy within that predetermined volume. The panel2000 may include one or more of the above-described acoustic attenuationmaterials.

FIG. 21 is a flow diagram of a method of attenuating acoustic energy.Although the flow diagram illustrates particular steps in a particularorder, this is for exemplary purposes only and the order of the stepsmay be rearranged from that depicted in FIG. 21. The first step 2101includes placing a member in the path of acoustic energy to beattenuated. The member may comprise a porous polymer and supportmaterial. The porous polymer may include PTFE, urethane, polystyrene,silicone, fluoropolymer, polyolefin (e.g., polyethylene andpolypropylene) or a combination thereof.

The porous polymer may be in the form of one or more layers of wovenfibers. The support material may occupy a portion of the void spacebetween the woven fibers.

The porous polymer may be in the form of a plurality of individuallayers of non-woven sheets. For example, a plurality of layers of porouspolymer may be interleaved with a plurality of layers of supportmaterial. The sheets may be continuous or the sheets may be perforated.In embodiments where the sheets are perforated, the support material mayat least partially fill the perforations.

The placing may include placing the member adjacent to a surface where afront side of the member is in contact with the surface. The placing mayinclude placing the member within a predetermined volume to dampacoustic energy within the predetermined volume.

The second step 2102 may be to absorb at least a portion of the acousticenergy within the member. In embodiments where the member is placedadjacent to a surface, the absorbing may include absorbing acousticenergy emanating from the surface and absorbing acoustic energy incidentof a rear side of the member within the member.

The third step 2103 may be to support the porous polymer with thesupport material. This may, for example, be achieved my encapsulating alayer of woven porous polymer within a matrix of support material, or byinterleaving a plurality of layers of porous polymer with a plurality oflayers of support material.

FIG. 22 is a flow diagram of a method of reducing acoustic energyincident on a back face of an ultrasound transducer. Although the flowdiagram illustrates particular steps in a particular order, this is forexemplary purposes only and the order of the steps may be rearrangedfrom that depicted in FIG. 22. The acoustic energy may have a frequencybetween 100 kHz and 100 MHz.

The first step 2201 includes providing a layer of material comprising aporous polymer. The porous polymer may be woven or non-woven. The layerof material may have a front surface and a rear surface. The layer ofmaterial may also include support material. In embodiments includingwoven porous polymers, a layer of woven porous polymer may beencapsulated within a matrix of support material.

In embodiments including non-woven porous polymer, the non woven porouspolymer may be in the form of a plurality of sheets interleaved with aplurality of sheets of support material. The sheets may be continuous orthe sheets may be perforated. In embodiments where the sheets areperforated, the support material may at least partially fill theperforations.

The second step 2202 may be to locate the material so that the frontsurface of the material is adjacent to a back face of an ultrasoundtransducer in a face-to-face relationship. The back surface of thematerial may be in contact with a fluid such as a gas. The fluid may,for example, be air contained within an ultrasound probe casing orwithin a catheter that contains an ultrasound transducer.

The next step 2203 may be to absorb acoustic energy emanating from theback face of the ultrasound transducer. The following step 2204 may beto absorb acoustic energy incident upon the rear surface of thematerial. In this regard, the absorbed energy may be prevented fromreaching the back face of the ultrasound transducer and interfering withthe operation of the ultrasound transducer.

Although the above detailed description generally describes embodimentsrelated to acoustic attenuation materials and ultrasound probeassemblies, embodiments described herein may be utilized in otherapplications where acoustic attenuation is desired and in otherultrasonic transducer configurations.

Additional modifications and extensions to the embodiments describedabove will be apparent to those skilled in the art. Such modificationsand extensions are intended to be within the scope of the presentinvention as defined by the claims that follow.

The invention claimed is:
 1. Acoustic attenuation material comprising: afirst side; a second side oppositely disposed from said first side; apolymer having a porosity, said polymer comprising at least one of awoven layer having a porosity and a non-woven membrane having aporosity; and a reinforcing material, wherein acoustic attenuation ofsaid polymer is at least twice that of said reinforcing material,wherein said reinforcing material has a flexural modulus greater thanthat of the polymer having a porosity, and wherein said polymer and saidreinforcing material are configured such that a sound beam travelingfrom said first side to said second side must pass through at least aportion of said polymer.
 2. The acoustic attenuation material of claim1, wherein said polymer having said porosity has a first flexuralmodulus; and wherein said acoustic attenuation material has an overallflexural modulus of at least twice that of said first flexural modulus.3. The acoustic attenuation material of claim 2, wherein saidreinforcing material has a second flexural modulus, and wherein saidfirst flexural modulus is less than 20 Mpa and said second flexuralmodulus is at least 40 Mpa.
 4. The acoustic attenuation material ofclaim 1, wherein said polymer is selected from a group consisting ofPTFE, urethane, polystyrene, fluoropolymer, silicone and polyolefin,wherein said reinforcing material is selected from a group consisting ofpolymer, ceramic and metal.
 5. The acoustic attenuation material ofclaim 1, wherein said reinforcing material is selected from a groupconsisting of epoxy, THV, FEP, PTFE, PES, EFEP, PET, PEEK, PEI, PC andLCP.
 6. The acoustic attenuation material of claim 1, wherein saidporosity is at least 5 percent.
 7. The acoustic attenuation material ofclaim 1, wherein said acoustic attenuation material has an acousticattenuation of at least 25 dB/em at 1 MHz with respect to soundtraveling from said first side to said second side.
 8. The acousticattenuation material of claim 1, wherein said porosity is partiallyfilled with said reinforcing material.
 9. The acoustic attenuationmaterial of claim 8, wherein said polymer comprises a woven layer havingvoids at least partially filled with said reinforcing material.
 10. Theacoustic attenuation material of claim 9, wherein said reinforcingmaterial encapsulates said woven layer.
 11. The acoustic attenuationmaterial of claim 1, wherein said polymer comprises a plurality ofnon-woven membranes, wherein said reinforcing material comprises aplurality of support layers, and wherein said plurality of non-wovenmembranes are interleaved with said plurality of support layers.
 12. Theacoustic attenuation material of claim 11, wherein each of saidplurality of non-woven membranes comprises a plurality of vias defininga plurality of passageways through said plurality of non-wovenmembranes, wherein at least a portion of said plurality of vias arefilled with said reinforcing material.
 13. The acoustic attenuationmaterial of claim 12, wherein said porous polymer is selected from agroup consisting of PTFE, urethane, polystyrene, fluoropolymer,silicone, and polyolefin.
 14. The acoustic attenuation material of claim13, wherein said reinforcing material is selected from a groupconsisting of epoxy, THV, FEP, PTFE, PES, EFEP, PET, PEEK, PEI, PC, andLCP.
 15. The acoustic attenuation material of claim 11, wherein each ofsaid plurality of membranes has a thickness less than 800 microns,wherein each of said plurality of support layers has a thickness lessthan 500 microns.
 16. The acoustic attenuation material of claim 1,wherein said polymer comprises at least one non-woven membrane, andwherein said reinforcing material comprises at least one support layercomprising a different polymer.
 17. The acoustic attenuation material ofclaim 1, wherein said polymer comprises at least one membrane comprisingPTFE and having a first flexural modulus, and wherein said reinforcingmaterial comprises at least one support layer having second flexuralmodulus at least twice the first flexural modulus.
 18. Acousticattenuation material comprising: a first side; a second side oppositelydisposed from said first side; a polymer having a porosity, said polymercomprises a plurality of non-woven membranes; and a reinforcingmaterial, wherein acoustic attenuation of said polymer is at least twicethat of said reinforcing material, wherein said reinforcing material hasa flexural modulus greater than that of the polymer having a porosity,wherein said reinforcing material comprises a plurality of supportlayers, wherein said plurality of non-woven membranes are interleavedwith said plurality of support layers, and wherein said plurality ofnon-woven membranes and said plurality of support layers are configuredsuch that a sound beam traveling from said first side to said secondside must pass through at least a portion of said plurality of non-wovenmembranes.
 19. The acoustic attenuation material of claim 18, whereineach of said plurality of non-woven membranes comprises a plurality ofvias defining a plurality of passageways through said plurality ofnon-woven membranes, wherein at least a portion of said plurality ofvias are filled with said reinforcing material.
 20. The acousticattenuation material of claim 18, wherein said porosity is partiallyfilled with said reinforcing material.
 21. The acoustic attenuationmaterial of claim 18, wherein each of said plurality of membranes has athickness less than 800 microns, wherein each of said plurality ofsupport layers has a thickness less than 500 microns.